Mikuni vs Dyno Jet

[lhanscom]

Are Mikuni and Dyno Jet main jet size numbers the same? I have a Dyno jet kit in my carbs right now, and need to go up a size in the mains, so I'll probably end up getting mikuni jets instead. The jets in it right now are 130's and I'm thinking 132.5's are what I need. Also, the way I've diagnosed this is that, at highway speeds holding constant throttle, it surges. I'm right to think this is the mains right?

[Billy Ricks]

Could be needle heighth as well. Mikuni mains will work with the Dynojet kits.

[lhanscom]

Would the needle be involved when doing 75mph, and around 5800rpm? I was thinking it would be all on the mains. Thanks for your help.

[Billy Ricks]

You're still on the needles at that point and the size of the mains shouldn't have that great an influence. The mains take over at about 3/4 throttle. There is some overlap but at 5,800 you're on the needles. Most upper rpm problems are from too rich of a mixture.

[lhanscom]

Very good, how much would you raise the needles? Full notch, half notch?

[Billy Ricks]

The only way to know for sure which way to go is with a plug reading. You may actually need to drop them. Go a half at a time. I know it's a pain to keep pulling the carbs but that is what you go through to get the jetting as good as it can be.

[lhanscom]

Well at least I have the weekend to tinker with it, although the nice weather is going away again for a while, got all the way up to 50. Thanks alot for the info, and by the way, the pipe sounds great.

[KEITH KRAUSE]

From my experience,if you can feel surging at 75 mph,I would try a full notch richer. Surging usually means you're beyond a 1/2 step from perfect. I have seen bikes that are running pretty good at that speed,and have no noticable surging,but when you take a plug read,they are still a light gray. It is always better to error a bit on the rich side. KK.

[Don Lobacz]

Dynojet and mikuni numbers are not the same. 138 in a dynojet would probably be 115 in Mikuni.

[Jeff Tate]

Yep! Surging usually means too lean. Raise the needles a full notch and see how she reponds.

[Billy Ricks]

It's been a while since I ran the stock carbs with the Dynojet kit and I don't have them anymore. But, I believe the Dynojet mains were 116's and when I switched to Mikuni mains I was running either 125's or 130's.

[lhanscom]

Thanks for all the info, I raised the needles 1 notch, figuring if I went too far I could just go back half notch. Anyway, it's too cold to go for a ride, so I can't tell if the surging bit is gone, but now when I crack the throttle and raise the rpms to 4000 or so and hold it, it sounds like it wants to back fire. It doesn't actually make a big explosion, just a bunch of little pops, making it sound kinda crackley. Also, I looked at my plugs, but unfortunatly, the last 20 mi of my ride is back roads, and I wasn't experienceing surging there. So my plugs didn't look too bad. Thoughts???